1. Field of the Invention
This invention relates to improvements in method and means for forming spirally fluted tubes and more particularly, but not by way of limitation, to apparatus for forming variable depth spiral grooves around the outer periphery of the tube and controlling the outer diameter of the tube during the fluting operation.
2. Description of the Prior Art
Finned tubes have long been utilized in the heat exchanger industry, and the like, for improving the dissipation of heat. Many of the tubes in use today comprise a cylindrical tube having a plurality of longitudinally spaced radially extending fins secured to the outer periphery thereof, and in some instances the tubes are provided with a continuous helical fin secured to the outer periphery of the tube. The inner periphery of these tubes is normally smooth and whereas the fins on the outer periphery of the tube improve the operation of the heat exchanger, the inner periphery does not provide any material increased effect in the efficiency of the tube. It has been found that twisting of the walls of the tube itself in order to deform the tube into a helical corrugated configuration along the length thereof provides an even more efficient heat dissipation in a heat exchanger in that both the inner and outer peripheries of the tube are deformed. These twisted tubes have certain disadvantages, however, in that it is difficult to control the dimensions of the outer diameters thereof, thus creating a problem in the installation of a plurality of the tubes in a heater, or the like, having predrilled or preformed bores therein for receiving the tubes therethrough. In addition, it is substantially impossible to predetermine a depth for the fluting or spiral groove formed by the tube twisting operation, and the tube twisting operation is completely ineffective in the event it is desirable to provide a tube having alternate grooves sections and smooth walled sections.